CO oxidation on Ni doped and Ni-M (M = Ca, Sc, V, Cu) bimetal-doped graphene: A first-principles study

CO oxidation over atomic Ni doped and Ni-M (M = Ca, Sc, V, Cu) bimetal-doped graphene (Ni@graphene and Ni-M@graphene, respectively) were investigated by first-principles method. For atomic Ni@graphene, O-2 is adsorbed first and then reacts with CO (gas phase) directly to release the first CO2. The barrier is about 0.432 eV. The remaining O atom would react with CO (gas phase) directly and release the second CO2 with a barrier of 0.368 eV. If another metal atom was doped at the opposite site of Ni atom, the reaction path does not change. However, the calculated reaction barriers are all higher for the first CO2 release but lower for the second. The CO and O-2 co-adsorption structures are all energetically unfavorable. The reason is that the LUMO orbital of the O-2 pre-adsorbed structure is mainly located on the two O atoms, and thus will have a maximum overlap with the CO HOMO orbital. D-band model can explain the different adsorption energies for CO and O-2.